Prof. K. Ganapathy
InnovaSpace Advisory Board member, Past President Telemedicine Society of India, Former Secretary/Past President Neurological Society of India & Indian Society for Stereotactic & Functional Neurosurgery, Emeritus Professor Tamilnadu Dr MGR Medical University, Former Adjunct Professor IIT Madras & Anna University Madras, Founder Director, Apollo Telemedicine Networking Foundation & Apollo Tele Health.
Three decades ago even contemplating the subject of the human brain in space would have been considered preposterous. Two decades hence and Extra Terrestrial Neurosciences could become a distinct sub-speciality. With periods of stay in the International Space Station steadily increasing, manned missions to the Moon being revived, and even humans going to Mars being seriously planned, it is imperative we know what happens structurally and functionally to various parts of the human brain when it is exposed to microgravity and cosmic radiation for prolonged periods. This is no longer a theoretical academic discussion. For decades we have relied on experimental simulation studies on the brains of rats exposed to microgravity and cosmic radiation. Mice exposed for six months to the radiation levels prevalent in interplanetary space exhibited serious memory and learning impairments, also becoming more anxious and fearful. Structural changes at a microscopic level, including changes in neurotransmitters were demonstrated.
It is only in the last decade that reliable, prospective clinical and sophisticated imaging studies have been carried out on astronaut brains before and after exposure to real world conditions. The human brain was primarily designed for standing in gravity on Earth with almost no exposure to radiation. When we leave the Earth’s gravitational pull all bodily fluids move upward. The first evidence for structural changes in the brain after long-term spaceflight includes narrowing of the central sulcus, a shrinking of the cerebrospinal fluid (CSF) spaces at the vertex, and an upward shift of the brain. MRI scans before spaceflight, shortly after and several months after return to Earth revealed a significant increase in size of the lateral and third ventricles immediately post-flight and a trend towards normalization at follow-up. There was an upward shift of the brain after all long-duration flights. Significant volumetric gray matter decreases, including large areas in the temporal and frontal poles and around the orbits have been documented. This effect was more noticeable in crewmembers with prolonged stay in the International Space Station. Bilateral focal gray matter increases within the medial primary somatosensory and motor cortex (cerebral areas representing lower limbs) were noted. Cortical reorganization in an astronaut’s brain after long-duration spaceflight has now been confirmed.
MRI documented structural changes raise the risk of possible impairment of behaviour, cognition and performance. This could compromise mission critical decisions. In 2017, a study revealed that long missions in space results in reduction of protective CSF surrounding brain volume at the top of astronauts’ brains. These changes underlie the astronauts’ performance on certain critical tasks, such as opening the space station’s hatch, climbing a ladder, exiting a vehicle or even walking along the surface of a planet. Follow up MRI scans have revealed that re-exposure to Earth’s gravity and lack of continuing exposure to unnatural radiation can generally reverse these space travel induced changes. Astronauts have to undergo extensive training before and during spaceflight to maintain muscle mass, and this can result in localised increased grey matter, particularly in the sensorimotor regions of the brain, representing the lower limbs. This is due to neuroplasticity or adaptation within the cerebrum and cerebellum.
The most notable findings in the MRI’s were a post-flight increase in the stimulation-specific connectivity of the right posterior supra marginal gyrus with the rest of the brain; a strengthening of connections between the left and right insulae, decreased connectivity of the vestibular nuclei, right inferior parietal cortex and cerebellum with areas associated with motor, visual, vestibular, and proprioception functions. Study of permanent visual acuity impairments associated with spaceflight have demonstrated structural changes in the CSF around the optic nerves and the globe of the eyes.
Domain expertise in Extra Terrestrial Neurosciences will eventually be a reality. While the number of subjects studied may at the best be a few hundreds, the lessons learnt could make us relook at the traditional neurosciences we have been believing in for the last two centuries.
Let us never forget that the future is always ahead of schedule !!